January 1, 2000 - December 31, 2002
Funding Agency: CALFED


Investigators: Don Weston ¹, Inge Werner ²,
Kathi Kuivila ³, Mike Lydy ⁴, Bill Jennings ⁵
(please reference below)

Project Summary:

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Populations of many aquatic species in the delta are in decline. This decline has been attributed to a number of factors (dams, water diversions, loss of habitat, exotic organisms), but toxic contaminants have often been among the suggested. Laboratory bioassays have identified pesticides, in particular organophosphate insecticides, as the major causes of toxicity detected in Delta water samples. Toxicity of water samples to bioassay organisms has been linked to pesticides and metals in the Sacramento River, and to pesticides in storm irrigation runoff from row and orchard crops in the San Joaquin River Basin.

There is, however, a fundamental difficulty in trying to use existing data to predict pesticide effects either on fish or their invertebrate prey in the Delta. Nearly all work to date has involved: 1) monitoring of dissolved pesticide concentrations and comparison to published toxicity data; and 2) toxicity testing using nationally standardized tests, most commonly with Ceriodaphnia dubia. The fundamental problem with such an approach is that literature toxicity data does not take into account local conditions like interactive effects of multiple pesticides, acclimation or sensitization due to prior pesticide exposure, of bioavailablity limitations attributable to factors such as dissolved organic matter. Thus the literature values may be dramatically different than the concentrations that are actually toxic in Delta waters. Moreover, there is no information on how pesticide sensitivity of C. dubia compares to that of resident species. This is an integrated laboratory and field study with the objectives of providing information on pesticide toxicity to resident species, developing the data needed to apply laboratory-derived toxicity measures to realistic field conditions, and putting results in an ecological context focusing on juvenile chinook salmon and their invertebrate prey.

The emphasis on chinook salmon is an important part of the overall project. There is reason to believe that pesticides in the Delta may be having direct toxic effects on the juveniles that are in the system during winter periods of high pesticide concentration. It has been found, for example, that diazinon concentrations on the order of those reported in the Sacramento and San Joaquin Rivers impair olfactory function in Atlantic. Pesticide effects on salmon may be indirect as well, for juvenile chinook in the Delta feed upon dipterans, cladocerans, copepods and amphipods, which as arthropods may be particular sensitive to pesticide toxicity.

The magnitude, timing and geographic extent of observed toxicity suggests that pesticide effects on resident species populations, either through direct toxicity or indirectly through loss of prey organisms, is a high priority area for investigation if restoration of the Bay-Delta is to be successful.


Our Study has the following objectives:

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• Conduct an initial data review to identify pesticides of concern and field sites;


• Develop toxicity tests with resident species, focusing on chinook salmon and their prey, and chronic endpoints such as abnormal development, growth, cellular effects, immune system effects, and target enzyme inhibition;


• Evaluate the influence of local conditions (e.g., pesticide mixtures, organic matter) on pesticide bioavailablity and/or toxicity in order to enhance interpretation of existing monitoring data;


• Assess toxicity under realistic exposure conditions in which multiple pesticide pulses vary in magnitude, frequency and duration;


• Conduct a comprehensive field study in which we well: 1) determine magnitude and duration of toxic pulses at selected sites; 2) demonstrate the effect of pesticide on resident aquatic species in both lab and in situ exposures; 3) determine the pesticide(s) causing toxicity to these resident species through Toxicity Indentification Evaluations; and 4) examine salmonid diet composition throughout these pesticide events link invertebrates impacts to habitat trophic value for fish.


• Integrate existing information and data development through these studies to formulate recommendations for a pesticide monitoring and management strategy in the Delta.

References:

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¹ Richmond Field Station, University of California, Berkeley, CA
² Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, UC Davis, CA
³ U.S. Geological Survey, Sacramento, CA
⁴ Department of Biological Sciences, Wichita State University, Kansas
⁵ DeltaKeeper, Stockton, CA



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